Thanks to the power of blogging & IRC, after mentioning about how I'd like native continuation support in the JVM for building web apps, workflow apps & better asynchronous distributed systems along come 2 solutions.

The first Torsten mentioned this blog entry which demonstrates using Brakes with Cocoon which looks neat. Then in IRC Geert Bevin mentioned RIFE
which does a similar thing. It appears Rife targets specific action
classes inside a class loader for bytecode modification. Both Brakes
and Rife deserve a closer look; they both look close to just what I
need.